Psychometric Evaluation of the 15-Item Five Facet Mindfulness Questionnaire: A Cross-Cultural Comparison Study Among English- and Chinese-Speaking Adult Mental Health Service Users

<b>Objectives</b>: Mindfulness has been proposed as an important health outcome and an indicator of mental well-being. This study aimed to evaluate the psychometric properties of the Five Facet Mindfulness Questionnaire (FFMQ-15) in two samples of mental health service users with diverse cultural and linguistic backgrounds (English- and Chinese-speaking). The study addresses the conceptual gap regarding the limited validation of the FFMQ-15 in Chinese-speaking clinical populations and examines the implications of measurement invariance. This study aimed at (1) confirming the reliability and validity of the FFMQ-15 in mental health service users; (2) assessing the validity of the FFMQ-15 in Chinese-speaking populations, where evidence is limited; and (3) examining measurement invariance across English- and Chinese-speaking groups to ensure cross-cultural applicability and comparable score interpretation. <b>Methods</b>: Participants were recruited using snowball sampling and social media advertising, targeting adults aged 18 or older who could read and write English or Chinese and had received mental health services. The English-speaking sample comprised 115 adults, and the Chinese-speaking sample included 118 adults. Exploratory factor analysis was used to identify structural dimensions, while confirmatory factor analysis was conducted for both samples to evaluate the five-factor structure of the FFMQ-15. <b>Results</b>: The EFA showed literature-aligned results supporting the 5-factor structure model, while the CFA model demonstrated acceptable fit: χ²/df = 159.50/80 = 1.99, <i>p</i> < 0.001; CFI = 0.927; TLI = 0.904; RMSEA = 0.065 (90% CI [0.050, 0.080]); SRMR = 0.060, BIC = 10,843.067, meeting established thresholds, and the non-significant measurement variance indicated the measurement model's consistency among clinical patients and across different cultural contexts. <b>Conclusions</b>: The FFMQ-15 shows strong psychometric properties for measuring mindfulness in English- and Chinese-speaking mental health service users, supporting its value in clinical research and practice.